In this study, the natural radioactivity level and its effects on the environment of Lake Van, which is the largest lake in Turkey, were investigated extensively. Initially, 254 soil samples have been collected from the districts (Tusba, Edremit, Gevas, Tatvan, Ahlat, Adilcevaz, Ercis) located around the coastline of Lake Van in eastern Turkey. A Na(TI) detector was used to detect activity concentrations of radium (Ra-226), thorium (Th-232) and potassium (K-40) in each collected soil sample. The obtained average results were compared with available data from Turkey and international data base. The average activity in soil samples was measured as 28.0 +/- 3.7-43.6 +/- 2.2 Bq/kg for Ra-226, 27.3 +/- 4.1-55.4 +/- 4.8 Bq/kg for Th-232 and 377 +/- 42- 706 +/- 40 Bq/kg for K-40. It was observed that the average concentrations of Ra-226, Th-232, K-40 (43.6 +/- 2.2, 55.4 +/- 4.8, 706 +/- 40 Bq/kg, respectively) for Tatvan district and (37.0 +/- 3.5, 51.4 +/- 4.2, 479 +/- 41 Bq/kg, respectively) for Ahlat district were higher than both national and international average value. In addition, radiological effect parameters originating from terrestrial natural radionuclides for the study area; gamma dose rate (D-out), annual effective dose equivalent (AEDE), and lifetime cancer development probability (LCR) were calculated. The D-out, AEDE, LCR (83.0 +/- 3.9 nGy/h, 0.102 +/- 0.005 mSv/y, 0.36 +/- 0.02 x 10(-3), respectively) parameters in Tatvan district were found to be above the international allowable value.